1. Field of Invention
The present invention relates to a semiconductor device, and more generally to a resistance memory device.
2. Description of Related Art
Non-volatile memory is capable of saving stored data after the power is turned off and is thus an indispensable memory device for many electronic products to function properly. Currently, resistive random access memory (RRAM) is a type of non-volatile memory that is being actively developed in the industry. RRAM has low write-in operation voltage, short write in erase time, long memorizing time, non-destructive read out, multi-state memory, simple structure, and small required area. Consequently, RRAM has great potential in the applications in personal computers and electronic apparatuses in the future.
However, still lots of challenges need to be improved before the mass production of RRAM. One of the challenges is the variation of RRAM operation IV characteristics. The variance comes from possible multi-paths for filament formation. A wider electrode creates more possible paths for filament formation and therefore increases the variation of RRAM operation IV characteristics. In order to minimize said variation, the straightforward action is to scale down the electrode. However, due to the lithography resolution limit, it has been difficult to further narrow down the electrode.
On the other hand, at least two patterning steps are required to form a conventional RRAM. A first patterning step is performed to form a conductive plug in a dielectric layer. Thereafter, a second patterning step is performed to form a variable resistance cell constituted by a bottom electrode, a variable resistance layer and a top electrode. However, the two different patterning steps have their respective critical dimension (CD) variations. Besides, it is necessary to take the alignment error between the two different patterning steps into consideration. Both considerations increase the size of the resistance memory cell.